A downlight of a store, a projector light source, a head lamp (such as a headlight) of an automobile and the like are cited as a special lighting source, and a halogen lamp, a high-pressure mercury lamp, a metal halide lamp, and the like are used as these light sources. Among others, an arc discharge is used in high intensity discharge lamps such as the high-pressure mercury lamp and the metal halide lamp, so that light having higher directivity can be radiated with high efficiency and high output. However, these light sources have problems in that time necessary for stabilization after lighting is long, that an environmental load increases because of inclusion of mercury, and that time until luminance defined as a lifetime is reduced to a half is short.
In recent years, there is actively developed the light source in which a semiconductor luminescence element such as a light emitting diode (LED) and a semiconductor laser is used as a component for the light source or an excitation light source. There are proposed various configurations as the configurations of the light source in which the semiconductor luminescence element is used. Examples of the configurations include a configuration using the semiconductor luminescence element in which an emission wavelength is changed in a range of visible light (430 nm to 670 nm) by changing a semiconductor material or a composition, is used and a configuration in which the emission wavelength or an emission spectrum is changed to a desired wavelength by the combination of the semiconductor luminescence element and the phosphor.
For example, PTL 1 and PTL 2 propose a light source in which LEDs or semiconductor lasers emitting blue light, green light, and red light are combined. The light source of PTL 1 and PTL 2 is particularly useful for display use because the light beams of three primary colors can individually be emitted any time unlike conventional high-luminance discharge lamp. However, because the LED has a large spread angle of the output light and a large area of a light emitting unit, light utilization efficiency is low in an optical system constituting the light source, and a light output intensity of the light source cannot be increased. Although the semiconductor laser has a small spread angle of the output light and a small area of the light emitting unit, the output light has higher coherence. Therefore, in the case where the light source configured by the semiconductor laser is used in the display, there is a problem in that image quality is degraded due to a speckle noise in a green region and a red region.
In order to solve the above problems, there is proposed a method in which the speckle noise is suppressed while the light utilization efficiency is increased by a combination of semiconductor laser, a light emitting diode, and a phosphor or a combination of the semiconductor laser and the phosphor.
For example, PTL 3 proposes a light source in which a semiconductor laser (blue laser) that radiates blue light, a Y3(Al,Ga)5O12 phosphor (green phosphor), and a red light emitting diode are combined. PTL 4 proposes a light source in which the blue laser, the Y3(Al,Ga)5O12 phosphor (green phosphor), and a (Sr,Ca,Al,Si,N) phosphor (red phosphor) are combined. Further, PTL 5 proposes a configuration of a light source in which all the three primary colors are constituted by fluorescent light beams by combining a semiconductor luminescence element radiating ultraviolet light and a disc in which red, green, and blue phosphor layers are provided in parallel.
The conventional light emitting apparatus of PTL 5 will be described below with reference to FIG. 22.
As illustrated in FIG. 22, the conventional light emitting apparatus includes light emitting diode 1003 that emits ultraviolet light and color wheel 1004 in which phosphor layers including red, green, and blue phosphors are disposed in each compartmented region. The light radiated from light emitting diode 1003 is sequentially converted into red light, green light, and blue light by the rotation of the color wheel, and the color wheel is driven such that white light is radiated in the case where the light is observed on temporally average. According to the configuration of FIG. 22, (Sr,Ca,Ba,Mg)10(PO4)6C12:Eu or (Ba,Mg)Al10O17:Eu is used as the blue phosphor, ZnS:Cu, Al, or (Ba,Mg)Al10O17:(Eu,Mn) is used as the green phosphor, and Y2O2S:Eu is used as the red phosphor.
In FIG. 22, 1005 designates an auxiliary optical element, 1006 designates a relay lens, 1007 designates a reflecting mirror, 1008 designates a prism, 1009 designates a spatial optical modulator, and 1010 designates a projector lens.